/*=========================================================================
 *
 *  Copyright Insight Software Consortium
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *         http://www.apache.org/licenses/LICENSE-2.0.txt
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 *
 *=========================================================================*/
#ifndef __itkVnlHalfHermitianToRealInverseFFTImageFilter_hxx
#define __itkVnlHalfHermitianToRealInverseFFTImageFilter_hxx

#include "itkHalfHermitianToRealInverseFFTImageFilter.hxx"
#include "itkImageRegionIteratorWithIndex.h"
#include "itkProgressReporter.h"
#include "itkVnlHalfHermitianToRealInverseFFTImageFilter.h"

namespace itk
{

template< class TInputImage, class TOutputImage >
void
VnlHalfHermitianToRealInverseFFTImageFilter< TInputImage, TOutputImage >
::GenerateData()
{
  // Get pointers to the input and output.
  typename InputImageType::ConstPointer inputPtr = this->GetInput();
  typename OutputImageType::Pointer outputPtr = this->GetOutput();

  if ( !inputPtr || !outputPtr )
    {
    return;
    }

  // We don't have a nice progress to report, but at least this simple line
  // reports the begining and the end of the process.
  ProgressReporter progress( this, 0, 1 );

  const InputSizeType inputSize = inputPtr->GetLargestPossibleRegion().GetSize();
  const OutputSizeType outputSize = outputPtr->GetLargestPossibleRegion().GetSize();
  const OutputIndexType outputIndex = outputPtr->GetLargestPossibleRegion().GetIndex();

  // Allocate output buffer memory
  outputPtr->SetBufferedRegion( outputPtr->GetRequestedRegion() );
  outputPtr->Allocate();

  unsigned int vectorSize = 1;
  for ( unsigned int i = 0; i < ImageDimension; i++ )
    {
    if ( !VnlFFTCommon::IsDimensionSizeLegal( outputSize[i] ) )
      {
      itkExceptionMacro(<< "Cannot compute FFT of image with size "
                        << outputSize << ". VnlHalfHermitianToRealInverseFFTImageFilter operates "
                        << "only on images whose size in each dimension is a multiple of "
                        << "2, 3, or 5." );
      }
    vectorSize *= outputSize[i];
    }

  // VNL requires the full complex result of the transform, so we
  // produce it here from the half complex image assumed when the output is real.
  SignalVectorType signal( vectorSize );
  ImageRegionIteratorWithIndex< OutputImageType > oIt( outputPtr,
                                                       outputPtr->GetLargestPossibleRegion() );
  unsigned int si = 0;
  for (oIt.GoToBegin(); !oIt.IsAtEnd(); ++oIt)
    {
    typename OutputImageType::IndexType index = oIt.GetIndex();
    if ( index[0] >= static_cast< typename OutputImageType::IndexValueType >( inputSize[0] ) )
      {
      // Flip the indices in each dimension
      for (unsigned int i = 0; i < ImageDimension; ++i)
        {
        if ( index[i] != outputIndex[i] )
          {
          index[i] = outputSize[i] - index[i] + 2 * outputIndex[i];
          }
        }
      signal[si] = std::conj( inputPtr->GetPixel( index ) );
      }
    else
      {
      signal[si] = inputPtr->GetPixel( index );
      }
    si++;
    }

  OutputPixelType *out = outputPtr->GetBufferPointer();

  // call the proper transform, based on compile type template parameter
  VnlFFTCommon::VnlFFTTransform< OutputImageType > vnlfft( outputSize );
  vnlfft.transform( signal.data_block(), 1 );

  // Copy the VNL output back to the ITK image. Extract the real part
  // of the signal. Ideally, the normalization by the number of
  // elements should have been accounted for by the VNL inverse
  // Fourier transform, but it is not. So, we take care of it by
  // dividing the signal by the vectorSize.
  for ( unsigned int i = 0; i < vectorSize; i++ )
    {
    out[i] = signal[i].real() / vectorSize;
    }
}
}
#endif
